1. Field of the Invention
The present invention is directed to an electrode device for intracorporeal stimulation of body tissue, particularly for intracardiac stimulation of heart tissue, of the type having an electrode cable containing at least one elongated, insulated conductor and terminating in an electrode head disposed at the distal end of the cable.
2. Description of the Prior Art
An electrode device of the type generally described above is disclosed in U.S. Pat. No. 3,911,928 wherein the surface of the electrode head partially consists of insulating material and partially consists of electrically conductive material, connected to the conductor, and thereby forming at least one stimulation surface. The head of this known electrode device is provided with a plurality of relatively small conductive surfaces in order to reduce the threshold value, and consequently to reduce energy consumption. This known electrode head has a core of electrically conductive material with preformed parts projecting from the core, with the spaces between these projecting parts being filled with electrically insulating material. The projecting, preformed parts can be strips, a helix, or dots, in order to achieve a strip-like or punctiform distribution of the stimulation area of the electrode head. This known electrode device has the disadvantage that it is complicated, and therefore expensive, to manufacture such an electrode head.
When using an electrode device of the type having an electrode head containing a plurality of small stimulation surfaces, good contact between these surfaces and the heart tissue to be stimulated is essential. In known devices of this type, this means that the insulating material, which constitutes a large part of the surface of the electrode head, must be highly biocompatible so as to reduce the risk of fibrotic tissue being deposited on the electrode head. Fibrotic tissue can grow into a thick layer on the stimulation surfaces, thereby increasing the distance between the stimulation surfaces and the heart tissue to be stimulated, and thereby increasing the stimulation threshold, and thus requiring more power in order to effect stimulation.